PATCH: fail to improve psymtab memory consumption

[Jim Blandy <jimb at zwingli dot cygnus dot com>]

As Daniel said...

2001-07-20  Jim Blandy  <jimb@redhat.com>

	* dwarf2read.c (dwarf2_build_psymtabs_hard): Doc fix.

Index: gdb/dwarf2read.c
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2read.c,v
retrieving revision 1.29
diff -c -r1.29 dwarf2read.c
*** gdb/dwarf2read.c	2001/07/05 16:45:48	1.29
--- gdb/dwarf2read.c	2001/07/20 21:15:51
***************
*** 977,982 ****
--- 977,1010 ----
    info_ptr = dwarf_info_buffer;
    abbrev_ptr = dwarf_abbrev_buffer;
  
+   /* We use dwarf2_tmp_obstack for objects that don't need to survive
+      the partial symbol scan, like attribute values.
+ 
+      We could reduce our peak memory consumption during partial symbol
+      table construction by freeing stuff from this obstack more often
+      --- say, after processing each compilation unit, or each die ---
+      but it turns out that this saves almost nothing.  For an
+      executable with 11Mb of Dwarf 2 data, I found about 64k allocated
+      on dwarf2_tmp_obstack.  Some investigation showed:
+ 
+      1) 69% of the attributes used forms DW_FORM_addr, DW_FORM_data*,
+         DW_FORM_flag, DW_FORM_[su]data, and DW_FORM_ref*.  These are
+         all fixed-length values not requiring dynamic allocation.
+ 
+      2) 30% of the attributes used the form DW_FORM_string.  For
+         DW_FORM_string, read_attribute simply hands back a pointer to
+         the null-terminated string in dwarf_info_buffer, so no dynamic
+         allocation is needed there either.
+ 
+      3) The remaining 1% of the attributes all used DW_FORM_block1.
+         75% of those were DW_AT_frame_base location lists for
+         functions; the rest were DW_AT_location attributes, probably
+         for the global variables.
+ 
+      Anyway, what this all means is that the memory the dwarf2
+      reader uses as temporary space reading partial symbols is about
+      0.5% as much as we use for dwarf_*_buffer.  That's noise.  */
+ 
    obstack_init (&dwarf2_tmp_obstack);
    back_to = make_cleanup (dwarf2_free_tmp_obstack, NULL);